1. Field of the Invention
The present invention generally relates to an inspection method, in particular for inspecting defects of peripheral region of wafer surface by emitting linear light on a wafer surface.
2. Description of the Related Art
Owing to the non-single crystal lattice induced by a proper temperature change within the crucible, a lot of micro crystal defects (growth defects) will appear at the wafer surface. These growth defects often affect the behavior of carrier in the semiconductors. In the past, the inspection of growth defects could be performed by human eyes, but this method has some disadvantages such as lower accuracy and lower precision. Moreover, the human eyes will get tired after long term operation, so it cannot be widely used for the high speed and high repetition inspection. In order to improve these disadvantages, the automatic optical inspection (AOI) method is recently well recommended.
Generally, two system types are used to inspect the surface defects; the bright field (BF) system and the dark field (DF) system. The reflected light and scattered light from wafer surface is received by CCD camera in BF and DF system, respectively. During the inspection of growth defects by using the BF system, most of light will be reflected and acquired by the CCD camera, so the over-exposure image will be generated, which causes the surface defects are difficult to be observed. On the contrary, only the scattered light (about 5% of reflected light) induced by micro surface defects will be received by CCD camera in the DF system, and then the normal defects images can be readily obtained. However, the non-uniformity of brightness will be produced by using the DF method. The other disadvantages, such as bad image quality and inconvenient operation, are also caused.